The present invention discloses a class of water soluble betaine copolymers which have been found to be improved drag reducing agents, especially in brine or acid solutions. These betaine copolymers are copolymers of acrylamide and N-(3 sulfopropyl)-N-methacrolyoxyethyl-N, N-dimethyl-ammonium betaine.
The betaines are a special class of zwitterions. These materials are self-neutralized and contain no counterions. Moreover, the positive and negative charges are separated by alkyl groups.
Carboxymethacrylate betaine monomers (I) and polymers (II) are well-known and disclosed in U.S. Pat. No. 2,777,872 (Jan. 15, 1957), U.S. Pat. No. 2,834,758 (May 13, 1958) and U.S. Pat. No. 2,846,417 (Aug. 5, 1958). ##STR2##
Carboxyvinylpyridine betaine monomers and homopolymers (III) have also reported [H. Ladenheim and H. Morowetz, J. Poly. Sci. 26, 251 (1957)]. ##STR3##
Sulfovinylpyridine betaine monomers and homopolymers (IV) and acrylamide copolymers are known [R. Hart and D. Timmerman, J. Poly, Sci. 28, 118 (1958)]. ##STR4##
The butylsulfobetaine of poly(2-vinylpyridine) is soluble in water, but the butylsulfobetaine of poly(4-vinylpyridine) is not. Both betaines are soluble in salt solution.
N-(3-sulfopropyl)-N-methacroyl-oxyethyl-N-N-dimethyl-ammonium betaine monomer and copolymer with acrylamide are disclosed in Ger. Auslegeschrift No. 1207630 for use as a viscosifier. The monomer and homopolymers are also reported in Polymer 25 121,254 (1984).
More recently, reports of vinylimidazolium sulfobetaine homopolymers (V) have appeared [J. C. Salamone, et al Polymer 18, 1058 (1977); Polymer 19, 1157 (1978)] ##STR5##
These homopolymers are insoluble in water, but soluble in certain salt solutions. In contrast to normal polyelectrolytes, the reduced viscosity of the soluble imidazolium sulfobetaine polymers increases with increasing salt concentration.